This invention relates generally to quartz crystal resonators for frequency control apparatus and the like and more particularly to a technique for accurately correcting the angles of cut of quartz crystal blanks or plates.
It is well known that quartz crystal plates utilized for frequency control apparatus cannot be cut with sufficient accuracy where high precision applications are intended. Thus following the initial cutting operation, the crystal blanks usually must have their orientation angles corrected prior to their installation in the respective equipment with which they are to be utilized.
In U.S. Pat. No. 3,803,774 entitled, "Technique For Correcting The Crystallo-Graphic Orientation Angle of Crystals by the Formation of Mesas and Double Face Lapping", issued to A. J. Miller on Apr. 16, 1974, several possible techniques are disclosed for correcting the angles of cut of quartz plates and involves first the formation of mesas by various techniques such as etching, machining, or mounting a chip on the surface of the plate, followed by a double face lapping operation until the mesas are removed, at which point the orientation angle has been changed the desired amount and the lapped surfaces of the plate are substantially parallel. An inherent problem, however, arises in the masking of the quartz plates during the etching process because the masking material itself is also subject to etching. Also the complexity of the method of applying and removing the masking materials themselves provides a limitation. Various tapes, photo-resists and solder resists have been evaluated by several investigators, but to date none has proved to be satisfactory. Chemical and ion etching has been suggested in U.S. Pat. No. 3,694,677, entitled, "VHF-UHF Piezoelectric Resonators", issued to G. K. Guttwein, et al. on Sept. 26, 1972. In U.S. Pat. No. 3,489,564, entitled, "Photolytic Etching of Silicon Dioxide" issued to D. L. Schaefer on Jan. 13, 1970, there is generally disclosed a photolytic process whereby etching of a predetermined pattern for decorative or optical purposes is achieved by exposing the surface of the body to be etched with radiation and which has been previously treated by a photolytically decomposable liquid; however, such a process has not heretofore been suggested for correcting the angles of cut of quartz resonators.
It is an object of the present invention, therefore, to provide an improvement in the method and apparatus for correcting the angles of cut of quartz resonator plates.
It is a further object of the present invention to provide an improvement in the formation of mesas on a quartz resonator plate for correcting the oeientation angles.
Still another object of the present invention is to provide an improvement in the method of etching at least one major face of a quartz resonator plate for correcting the angles of cut.